Microsoft Word C031262e doc Reference number ISO 899 1 2003(E) © ISO 2003 INTERNATIONAL STANDARD ISO 899 1 Second edition 2003 06 01 Plastics — Determination of creep behaviour — Part 1 Tensile creep[.]
ISO 899-1 INTERNATIONAL STANDARD Second edition 2003-06-01 `,,,`-`-`,,`,,`,`,,` - Plastics — Determination of creep behaviour — Part 1: Tensile creep Plastiques — Détermination du comportement au fluage — Partie 1: Fluage en traction Reference number ISO 899-1:2003(E) Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2003 Not for Resale ISO 899-1:2003(E) PDF disclaimer This PDF file may contain embedded typefaces In accordance with Adobe's licensing policy, this file may be printed or viewed but shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing In downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy The ISO Central Secretariat accepts no liability in this area Adobe is a trademark of Adobe Systems Incorporated Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation parameters were optimized for printing Every care has been taken to ensure that the file is suitable for use by ISO member bodies In the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below © ISO 2003 All rights reserved Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body in the country of the requester ISO copyright office Case postale 56 • CH-1211 Geneva 20 Tel + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyright@iso.org Web www.iso.org Published in Switzerland ii `,,,`-`-`,,`,,`,`,,` - Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2003 — All rights reserved Not for Resale ISO 899-1:2003(E) Contents Page Foreword iv Scope Normative references Terms and definitions Apparatus Test specimens Procedure Expression of results Test report `,,,`-`-`,,`,,`,`,,` - Annex A (informative) Physical-ageing effects on the creep of polymers 11 Bibliography 15 iii © ISO 2003 — All rights reserved Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale ISO 899-1:2003(E) Foreword `,,,`-`-`,,`,,`,`,,` - ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies) The work of preparing International Standards is normally carried out through ISO technical committees Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part The main task of technical committees is to prepare International Standards Draft International Standards adopted by the technical committees are circulated to the member bodies for voting Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights ISO shall not be held responsible for identifying any or all such patent rights ISO 899-1 was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 2, Mechanical properties This second edition cancels and replaces the first edition (ISO 899-1:1993), which has been technically revised ISO 899 consists of the following parts, under the general title Plastics — Determination of creep behaviour: Part 1: Tensile creep Part 2: Flexural creep by three-point loading iv Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2003 — All rights reserved Not for Resale INTERNATIONAL STANDARD ISO 899-1:2003(E) Plastics — Determination of creep behaviour — Part 1: Tensile creep Scope 1.1 This part of ISO 899 specifies a method for determining the tensile creep of plastics in the form of standard test specimens under specified conditions such as those of pretreatment, temperature and humidity 1.2 The method is suitable for use with rigid and semi-rigid non-reinforced, filled and fibre-reinforced plastics materials (see ISO 472 for definitions) in the form of dumb-bell-shaped test specimens moulded directly or machined from sheets or moulded articles 1.3 The method is intended to provide data for engineering-design and research and development purposes Data for engineering-design purposes requires the use of extensometers to measure the gauge length of the specimen Data for research or quality-control purposes may use the change in distance between the grips (nominal extension) 1.4 Tensile creep may vary significantly with differences in specimen preparation and dimensions and in the test environment The thermal history of the test specimen can also have profound effects on its creep behaviour (see Annex A) Consequently, when precise comparative results are required, these factors must be carefully controlled 1.5 If tensile-creep properties are to be used for engineering-design purposes, the plastics materials should be tested over a broad range of stresses, times and environmental conditions Normative references The following referenced documents are indispensable for the application of this document For dated references, only the edition cited applies For undated references, the latest edition of the referenced document (including any amendments) applies ISO 62:1999, Plastics — Determination of water absorption ISO 291:1997, Plastics — Standard atmospheres for conditioning and testing ISO 472:1999, Plastics — Vocabulary ISO 527-1:1993, Plastics — Determination of tensile properties — Part 1: General principles ISO 527-2:1993, Plastics — Determination of tensile properties — Part 2: Test conditions for moulding and extrusion plastics ISO 10350-1:1998, Plastics — Acquisition and presentation of comparable single-point data — Part 1: Moulding materials `,,,`-`-`,,`,,`,`,,` - © ISOfor2003 — All rights reserved Copyright International Organization Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale ISO 899-1:2003(E) ISO 11403-1:2001, Plastics — Acquisition and presentation of comparable multipoint data — Part 1: Mechanical properties Terms and definitions For the purposes of this document, the terms and definitions given in ISO 472 and the following apply 3.1 creep increase in strain with time when a constant force is applied 3.2 initial stress σ `,,,`-`-`,,`,,`,`,,` - tensile force per unit area of the initial cross-section within the gauge length NOTE σ = It is given by the equation F A where F is the force, in newtons; A is the average initial cross-sectional area within the narrow (gauge) section of the specimen, in square millimetres NOTE It is expressed in megapascals 3.3 extension (∆L)t increase in the distance between the gauge marks, expressed in millimetres, at time t NOTE It is given by the equation (∆L ) t = L t − L where Lt is the gauge length, in millimetres, at any given time t during the test; L0 is the original gauge length, in millimetres, of the specimen after application of a preload but prior to application of the test load Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2003 — All rights reserved Not for Resale ISO 899-1:2003(E) 3.4 nominal extension (∆L*)t increase in the distance between the grips (increase in grip separation) NOTE It is given by the equation (∆L∗) t = L∗t − L∗0 where L*t is the distance between the grips at any given time t during the test, in millimetres; L*0 is the initial distance between the grips, expressed in millimetres, holding the specimen after application of a preload but prior to application of the test load 3.5 tensile-creep strain εt change in the distance between the gauge marks, relative to the initial distance, produced by the applied load at any given time t during a creep test NOTE εt = NOTE It is given by the equation (∆L ) t L0 It is expressed as a dimensionless ratio or as a percentage 3.6 nominal tensile-creep strain ε*t change in the distance between the grips, relative to the initial distance, produced by the applied load at any given time t during a creep test NOTE ε ∗t = NOTE It is given by the equation ( ∆ L∗ ) t ∗ L It is expressed as a dimensionless ratio or as a percentage 3.7 tensile-creep modulus Et ratio of initial stress to tensile-creep strain, calculated as in 7.1.1 3.8 nominal tensile-creep modulus E*t ratio of initial stress to nominal tensile-creep strain, calculated as in 7.1.2 `,,,`-`-`,,`,,`,`,,` - 3.9 isochronous stress-strain curve Cartesian plot of stress versus creep strain, at a specific time after application of the test load 3.10 time to rupture period of time the specimen is under full load until rupture © ISO 2003 — All rights reserved Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale ISO 899-1:2003(E) 3.11 creep-strength limit initial stress which will just cause rupture (σ B,t) or will produce a specified strain (σε,t) at a specified time t, at a given temperature and relative humidity 3.12 recovery from creep decrease in strain at any given time after completely unloading the specimen, expressed as a percentage of the strain just prior to the removal of the load Apparatus 4.1 Gripping device, capable of ensuring that the direction of the load applied to the test specimen coincides as closely as possible with the longitudinal axis of the specimen This ensures that the test specimen is subjected to simple stress and that the stresses in the loaded section of the specimen may be assumed to be uniformly distributed over cross-sections perpendicular to the direction of the applied load NOTE It is recommended that grips be used that will allow the specimen to be fixed in place, correctly aligned, prior to applying the load Self-locking grips which allow the specimen to move as the load increases are not suitable for this test 4.2 Loading system, capable of ensuring that the load is applied smoothly, without causing transient overloading, and that the load is maintained to within ± % of the desired load In creep-to-rupture tests, provision shall be made to prevent any shocks which occur at the moment of rupture being transmitted to adjacent loading systems The loading mechanism shall allow rapid, smooth and reproducible loading 4.3 Extension-measuring device, comprising any contactless or contact device capable of measuring the extension of the specimen gauge length or the increase in the distance between the clamp grips under load without influencing the specimen behaviour by mechanical effects (e.g undesirable deformations, notches), other physical effects (e.g heating of the specimen) or chemical effects In the case of contactless (optical) measurement of the strain, the longitudinal axis of the specimen shall be perpendicular to the optical axis of the measuring device To determine the increase in length of the test specimen, an extensometer shall be used which records the increase in the distance between the clamp grips The accuracy of the extension-measuring device shall be better than ± 0,01 mm For creep-to-rupture tests, it is recommended that the extension be measured by means of a contactless optical system operating on the cathetometer principle Automatic indication of time to rupture is highly desirable The gauge length shall be marked on the specimen, either by attaching (metal) clips with scratchedon gauge marks, or by ruling the gauge marks with an inert, thermally stable paint Electrical-resistance strain gauges are suitable only if the material tested is of such a nature as to permit such strain gauges to be attached to the specimen by means of adhesive and only if the adhesion quality is constant during the duration of the test The modulus of the strain gauge when bonded to the specimen shall be such that the specimen is not reinforced 4.4 Time-measurement device, accurate to 0,1 % 4.5 Micrometer, reading to 0,01 mm or closer, for measuring the initial thickness and width of the test specimen Test specimens Use test specimens of the same shape and dimensions as specified for the determination of tensile properties by the relevant material standard or, by default, as specified in ISO 527-2 `,,,`-`-`,,`,,`,`,,` - Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2003 — All rights reserved Not for Resale ISO 899-1:2003(E) Procedure 6.1 Conditioning and test atmosphere `,,,`-`-`,,`,,`,`,,` - Condition the test specimens as specified in the International Standard for the material under test In the absence of any information on conditioning, use the most appropriate set of conditions specified in ISO 291, unless otherwise agreed by the interested parties The creep behaviour will be affected not only by the thermal history of the specimen under test, but also by the temperature and (where applicable) humidity used in conditioning If the specimen is not in humidity equilibrium, creep will be affected in the following way: a specimen which is too dry will produce an additional strain due to water absorption during the test and a specimen which is too humid will contract due to water desorption It is recommended that a conditioning time W t90 (see ISO 62) be used Conduct the test in the same atmosphere as used for conditioning, unless otherwise agreed upon by the interested parties, e.g for testing at elevated or low temperatures Ensure that the variation in temperature during the duration of the test remains within ± °C 6.2 Measurement of test-specimen dimensions Measure the dimensions of the conditioned test specimens in accordance with ISO 527-1:1993, Subclause 9.2 6.3 Mounting the test specimens Mount a conditioned and measured specimen in the grips and set up the extension-measuring device as required 6.4 Selection of stress value Select a stress value appropriate to the application envisaged for the material under test, and calculate, using the equation given in 3.2, the load to be applied to the test specimen If the initial strain is specified instead of the stress, the stress value may be calculated using Young’s modulus for the material (see ISO 527-1) 6.5 6.5.1 Loading procedure Preloading When it is necessary to preload the test specimen prior to increasing the load to the test load, for example in order to eliminate backlash by the test gear, take care to ensure that the preload does not influence the test results Do not apply the preload until the temperature and humidity of the test specimen (gripped in the test apparatus) correspond to the test conditions Measure the gauge length after application of the preload Maintain the preload during the whole duration of the test 6.5.2 Loading Load the test specimen smoothly so that full loading of the specimen is reached between s and s after the beginning of the application of the load Use the same rate of loading for each of a series of tests on one material Take the total load (including the preload) to be the test load © ISO 2003 — All rights reserved Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale ISO 899-1:2003(E) 6.6 Extension-measurement schedule Record the point in time at which the specimen is fully loaded as t = Unless the extension is automatically and/or continuously recorded, choose the times for making individual measurements as a function of the creep curve obtained from the particular material under test It is preferable to use the following measurement schedule: min, min, min, 12 and 30 min; h, h, h, 10 h, 20 h, 50 h, 100 h, 200 h, 500 h, 000 h, etc If discontinuities are suspected or observed in the creep-strain versus time plot, take readings more frequently 6.7 Time measurement Measure, to within ± 0,1 % or ± s (whichever is the less severe tolerance), the total time which has elapsed up to each creep measurement 6.8 Temperature and humidity control Unless temperature and relative humidity (where applicable) are recorded automatically, record them at the beginning of the test and then at least three times a day initially When it has become evident that the conditions are stable within the specified limits, they may be checked less frequently (but at least once a day) 6.9 Measurement of recovery rate (optional) Upon completion of non-rupture tests, remove the load rapidly and smoothly and measure the recovery rate using, for instance, the same schedule as was used for creep measurement Expression of results 7.1 Method of calculation 7.1.1 Tensile-creep modulus, Et Calculate the tensile-creep modulus, Et, by dividing the initial stress, σ, by the tensile-creep strain, εt, at each of the selected measurement times It is given, in megapascals, by the equation Et = F ⋅ L0 σ = εt A ⋅ (∆L ) t where F is the applied force, in newtons; L0 is the initial gauge length, in millimetres; A is the initial cross-sectional area, in square millimetres, of the specimen; (∆L)t is the extension, in millimetres, at time t `,,,`-`-`,,`,,`,`,,` - Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2003 — All rights reserved Not for Resale ISO 899-1:2003(E) 7.1.2 Nominal tensile-creep modulus, E*t Calculate the nominal tensile-creep modulus, E*t, by dividing the initial stress, σ, by the nominal tensile-creep strain, ε*t, at each of the selected measurement times It is given, in megapascals, by the equation E *t = σ ε *t = F ⋅ L*0 A ⋅ (∆L* ) t where F is the applied force, in newtons; L*0 is the initial distance between the grips, in millimetres; A is the initial cross-sectional area of the specimen, in square millimetres; (∆L*)t is the increase in the distance between the grips, in millimetres, at time t `,,,`-`-`,,`,,`,`,,` - 7.2 Presentation of results 7.2.1 Creep curves If testing is carried out at different temperatures, the raw data should preferably be presented, for each temperature, as a series of creep curves showing the tensile strain plotted against the logarithm of time, one curve being plotted for each initial stress used (see Figure 1) Key increasing stress Figure — Creep curves The data may also be presented in other ways, e.g as described in 7.2.2 and 7.2.3, to provide information required for particular applications 7.2.2 Creep-modulus/time curves For each initial stress used, the tensile-creep modulus, calculated in accordance with 7.1.1, may be plotted against the logarithm of the time under load (see Figure 2) © ISO 2003 — All rights reserved Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale ISO 899-1:2003(E) Key increasing stress Figure — Creep-modulus/time curves If testing is carried out at different temperatures, plot a series of curves for each temperature 7.2.3 lsochronous stress-strain curves An isochronous stress-strain curve is a Cartesian plot showing how the strain depends on the applied load, at a specific point in time after application of the load Several curves are normally plotted, corresponding to times under load of h, 10 h, 100 h, 000 h and 10 000 h Since each creep test gives only one point on each curve, it is necessary to carry out the test at, at least, three different stresses, and preferably more, to obtain an isochronous curve (see ISO 11403-1) To obtain an isochronous stress-strain curve for a particular time under load (say 10 h) from a series of creep curves as shown in Figure 1, read off, from each creep curve, the strain at 10 h, and plot these strain values (x-axis) against the corresponding stress values (y-axis) Repeat the process for other times to obtain a series of isochronous curves (see Figure 3) Key increasing time Figure — lsochronous stress-strain curves If testing is carried out at different temperatures, plot a series of curves for each temperature `,,,`-`-`,,`,,`,`,,` - Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2003 — All rights reserved Not for Resale ISO 899-1:2003(E) 7.2.4 Three-dimensional representation A relationship of the form ε = f (t,σ) exists between the different types of curve (see Figures to 3) that can be derived from the raw creep-test data This relationship can be represented as a surface in a three-dimensional space (see Reference [1] in the Bibliography) `,,,`-`-`,,`,,`,`,,` - All the curves that can be derived from the raw creep-test data form part of this surface Because of the experimental error inherent in each measurement, the points corresponding to the actual measurements normally not lie on the curves but just off them The surface ε = f (t,σ) can therefore be generated by deriving a number of the curves which form it, but a number of sophisticated smoothing operations are usually necessary Computer techniques permit this to be done rapidly and reliably 7.2.5 Creep-to-rupture curves Creep-to-rupture curves allow the prediction of the time to failure at any stress They may be plotted as stress against log time to break (see Figure 4) or log stress against log time to break Key increasing temperature NOTE The stress, σ, may also be plotted on a logarithmic scale Figure — Creep-to-rupture curves 7.3 Precision The precision of this test method is not known because interlaboratory data are not available When interlaboratory data are obtained, a precision statement will be added at the following revision Test report The test report shall include the following particulars: a) a reference to this part of ISO 899; b) a complete description of the material tested, including all pertinent information on composition, preparation, manufacturer, tradename, code number, date of manufacture, type of moulding and any annealing; c) the dimensions of each test specimen; © ISO 2003 — All rights reserved Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale ISO 899-1:2003(E) d) the method of preparation of the test specimens; e) the directions of the principal axes of the test specimens with respect to the dimensions of the product or some known or inferred orientation in the material; f) details of the atmosphere used for conditioning and testing; g) which tensile creep modulus, Et or E*t, was calculated; h) the creep-test data for each temperature at which testing was carried out, presented in one or more of the graphical forms described in 7.2, or in tabular form; i) if recovery-rate measurements are made, the time-dependent strain after unloading the test specimen (see 6.9) `,,,`-`-`,,`,,`,`,,` - 10 Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2003 — All rights reserved Not for Resale ISO 899-1:2003(E) Annex A (informative) Physical-ageing effects on the creep of polymers A.1 General Physical ageing takes place when a polymer is cooled from an elevated temperature at which the molecular mobility is high to a lower temperature at which relaxation times for molecular motions are long in comparison with the storage time at that temperature Under these circumstances, changes in the structure will take place over a long period of time, involving rearrangement in the shape and packing of molecules as the polymer approaches the equilibrium structural state for the lower temperature Associated with this ageing process, there is a progressive decrease in the molecular mobility of the polymer, even when the temperature remains constant As a direct consequence of this, the creep deformation produced by an applied stress will depend upon the age of the polymer, creep rates being lower in more highly aged material This is illustrated in Figure A.1 which shows creep compliance curves for PVC specimens of different ages Each of these specimens has been rapidly cooled from a temperature of 85 °C (close to Tg) and stored at the test temperature of 23 °C for different times te prior to load application The physical age of a specimen is then defined by the time te and it can be seen that the older the specimen the further its creep curve is shifted on the time axis A.2 Creep at elevated temperatures The influence of physical ageing on creep behaviour is more complicated when measurements are made at elevated temperatures following a storage period at a lower (ambient) temperature Under these circumstances, the physical ageing that takes place during storage at the lower temperature is temporarily reversed when the specimen is heated to the test temperature The rate at which this takes place depends on the size of the temperature change and the age of the specimen when the temperature is raised Following the reduction in the apparent (or effective) age of the specimen, physical ageing is reactivated at the higher temperature Again, the timescale over which this happens depends on the test conditions One consequence of these changes in age state caused by the temperature increase is thus a dependence of the creep behaviour at the elevated temperature on the dwell time at this temperature prior to load application Typical ways in which this type of thermal history influences creep compliance are illustrated in Figures A.2 and A.3 In Figure A.2, specimens were stored for a period te1 of 200 h at a temperature of 23 °C prior to heating to the test temperature of 44 °C Creep curves were then obtained after different periods te2 at 44 °C prior to load application Despite the relatively long storage period te1 at ambient temperature, the creep behaviour shows a strong dependence on the dwell time te2 In Figure A.3, creep tests were carried out under the same conditions but following a storage period te1 of greater than year at 23 °C prior to heating to the test temperature The progressive reduction in the effective age of the specimens is actually observed here as a shift in the curves to shorter creep times, and results from the more extensive structural changes that have taken place in the specimens through physical ageing before heating © ISO 2003 — All rights reserved Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS `,,,`-`-`,,`,,`,`,,` - Not for Resale 11 ISO 899-1:2003(E) `,,,`-`-`,,`,,`,`,,` - Figure A.1 — Creep curves for PVC at 23 °C obtained at different times te after rapid cooling of the specimen from 85 °C to 23 °C 12 Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2003 — All rights reserved Not for Resale ISO 899-1:2003(E) Figure A.2 — Creep curves for PVC at 44 °C obtained by application of the load at different times te2 after heating from 23 °C (the specimen had been stored for 200 h at 23 °C prior to heating) `,,,`-`-`,,`,,`,`,,` - 13 © ISOfor2003 — All rights reserved Copyright International Organization Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale ISO 899-1:2003(E) Figure A.3 — As for Figure A.2 but following storage for more than year at 23 °C prior to heating `,,,`-`-`,,`,,`,`,,` - 14 Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS © ISO 2003 — All rights reserved Not for Resale ISO 899-1:2003(E) Bibliography [1] TURNER, S., Creep in thermoplastics — Preliminary concepts and definitions, British Plastics, June (1964), pp 322-324 [2] LEHMANN, J., Zeitstandverhalten von PMMA in der Freibewitterung und im Normklima, V15 in 27 Jahrestagung der GUS, 18th March 1998, ISBN 3-9806167-0-3 `,,,`-`-`,,`,,`,`,,` - 15 © ISO 2003 — All rights reserved Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale ISO 899-1:2003(E) ICS 83.080.01 Price based on 15 pages `,,,`-`-`,,`,,`,`,,` - © ISO 2003 — All rights reserved Copyright International Organization for Standardization Provided by IHS under license with ISO No reproduction or networking permitted without license from IHS Not for Resale